This invention relates to a resilient member for use in side bearings, in particular, for side bearings deployed on railroad cars, typically freight cars. The invention also relates to a method of manufacturing the resilient members and the mold used in such manufacture.
Side bearings used on railroad vehicles, in particular railroad freight trucks, have taken many different configurations. Typically, such side bearings are used to control truck dynamic motion to minimize dynamic instabilities at higher operating speeds. More specifically, as railroad trucks become lighter and travel at higher speeds, dynamic instability tendencies increase, and it becomes necessary that such truck side bearings control such increased tendencies. These dynamic instabilities typically are referred to in the railroad industry as xe2x80x9ctruck hunting.xe2x80x9d
More specifically, a railroad truck""s hunting motion starts at the wheel/rail interface and is translated into the multi-body system of the railroad car. Thus, in order to minimize such hunting motion being translated into the multi-body system, side bearings are deployed as one of a multitude of suspension components, and serve multiple functions.
When mounted on a freight truck""s suspension, side bearings provide damping as a result of friction between the side bearing and car body. Further, the radial stiffness of most side bearings provides a more controlled connection between the wheels and the multi-body system.
In order to provide the above functions, side bearings rely on resilient members which make up part of the side bearing assembly. Such resilient members come in many shapes and forms, and each has its advantages and disadvantages.
One method of manufacture of such resilient members is through a transfer molding-type operation. More specifically, in such an operation, typically a resilient or elastomeric material (used interchangeably herein), such as rubber compound, is introduced into a mold through sprues located in a cap for the mold. The rubber compound is introduced under pressurized conditions to fill the mold which also contains metal elements covered with adhesive such that the rubber compound bonds to the metal. The compound is allowed to cure, and the resultant resilient member is then removed from the mold.
In conducting this operation, it is usually the case that the resilient member is weaker at the locations adjacent to where the sprues are located due to the inhomogeneity of the rubber compound in the area of the incoming flow. If such weakened regions occur at portions of the resilient member which receive the greatest stresses, forces and/or strains, such as on outer surface areas, the resilient member will often fail and break prematurely. This is especially true under extensive dynamic loading, such as in a suspension system. Similarly, when the cap is removed from the mold, as a result of rubber compound remaining in the sprue, weakened areas are created in the resilient material as the rubber compound sometimes breaks off beyond the end of the sprue and into the working body of the resilient member, making the resilient member non-usable or susceptible to stress concentrations and premature failure.
Thus, in accordance with the invention, the problems of the prior art are avoided, and a resilient member is provided having a unique geometry which is substantially less susceptible to failure than the resilient members currently in use. Further, a method and mold are provided which maintain the simplicity of prior methods and mold assemblies.
In accordance with one aspect of the invention, there is provided a resilient member, typically for use as an insert in a railway vehicle side bearing assembly. Although one skilled in the art will realize many other applications of the resilient member of the present invention. The resilient member includes a first rigid element extending in a linear direction, and having a first end and a second end. A second rigid element is disposed spaced substantially parallel to the first rigid element to provide a space between the first rigid element and the second rigid element. The second rigid element extends in the linear direction of the first rigid element, and includes a first end, with at least the first end displaced or offset along the linear direction away from the first end of the first rigid element. Resilient or elastomeric material fills the space between the first rigid element and the second element and adheres to the two elements. The resilient material extends between the first end of the first rigid element and the first end of the second element to define a predetermined, preferably substantially concave, profile between the two first ends. The resilient material also includes at a predetermined location at least one weakened region along the profile thereof. The weakened region a result of the resilient material being assembled with the first rigid element and the second rigid element, and adjacent to sprue locations in a mold. The weakened region is at a predetermined location on the resilient material which is subject to the lowest stress/strains when the resilient member is used as an insert in a side bearing assembly.
In another aspect, the invention relates to a method of making a resilient member which is used as an insert in a side bearing assembly. The method includes placing a first and a second rigid element in a mold with the first and second rigid elements extending in a linear direction and spaced, typically substantially parallel, from each other. As a result, a space is defined between the two elements. As noted previously, the first and second rigid elements each have a first end and a second end, with the first end of the first rigid element offset from the first end of the second rigid element. The first and second rigid elements have side surfaces substantially parallel to each other and facing each other. An adhesive is applied on the side surfaces of the first and second rigid elements which face each other, and resilient material is then forced into the mold through a cap having a predetermined, preferably substantially concave, profile surface extending between the first ends of the two rigid elements. The cap includes sprues spaced from each other around the periphery of the cap, and adjacent to the first end of the second rigid member. The resilient material is forced through the sprues into the mold. The sprues are positioned at a predetermined location of the lowest stress/strain in the resilient material of the dynamically loaded resilient member, and in the closest proximity to the second rigid element which allows the resilient material to be forced into the mold without stripping the adhesive off the side surface of the second rigid element. The resilient material is then cured in the mold to rigidify and have it adhere to the first and second rigid elements to result in the resilient member.
In another aspect, the invention relates to the mold for forming the resilient member. The mold includes a cap having sprues spaced about the periphery of the cap which allows the mold body to be filled with resilient or elastomeric material forced through the sprues under pressure. The sprues are positioned at a predetermined location of the lowest stress/strain in the resilient material of the dynamically loaded resilient member, and in the closest proximity to a rigid element in the mold while not stripping adhesive from the wall of the rigid element. The rigid elements in the mold may be, for example, flat or cylindrical elements previously placed in the mold for the purpose of manufacturing the resilient member or mount of the invention.